1. Field of the Invention
The present invention generally relates to a method and an apparatus for regulating exhaust pressure in an evacuation system of a semiconductor process chamber, and more particularly to a method and an apparatus for regulating exhaust pressure in an evacuation system of a semiconductor process chamber by use of an exhaust controller to control the gas flow rate introduced into the evacuation system.
2. Description of the Prior Art
Various semiconductor processes comprise treating wafers in a controlled evacuated environment, such as chemical vapor deposition process or plasma etching process. Such processes are generally carried out in a process chamber in which wafers are variously processed under a vacuum condition and an evacuation system connected to the process chamber. When the process starts, selected gases used for processing are mixed and introduced into the process chamber at rates according to the process recipe. Typically, during processing, pressures below one Torr need to be maintained in the process chamber. Therefore, the evacuation system continuously removes gases from the process chamber, and thereby maintains the desired pressure.
In general, a semiconductor evacuation system comprises lots of units such as pumps, scrubber, and valves. When independently implementing these units no surprising hardship exists if the application is satisfied with each requirement of the units, however, significant difficulties often arise from the application of integrating theses units. Thus, for an evacuation system, to achieve an optimum adjustment between these units is a way to improve the effectiveness of the evacuation system. The evacuation system typically comprises a turbo pump separated from the process chamber by a throttle valve. The throttle valve controlled by a pressure controller can be opened or closed to increase or decrease the vacuum supplied from the turbo pump to the process chamber for the purpose of maintaining the desired pressure in the process chamber. In this way, the pressure in the process chamber is controlled, but the pressure in the evacuation system (or pressure in the exhaust pipe) is not controlled likely leading to back diffusion, which may carry the particles back upstream to the process chamber contaminating the sidewall of the chamber or the wafer.
In the plasma etching process, for example, the reaction by-products such as particles and impurities are normally carried away (or exhausted) through the evacuation system to a scrubber for treatment before released to the atmosphere. However, some by-products are usually adhered to the inter-surface of the exhaust pipe or those of system units (such as pumps, and valves), once the equilibrium of the chamber pressure and the exhaust pressure is destroyed, a turbulent flow is likely occurred leading to the back diffusion of carrying particles back upstream to the process chamber causing product defects due to the contamination. Furthermore, the throttle valve is also a source of contamination for the chamber due to the accumulation of impurities and particles on its surface. During any pressure fluctuations in the chamber, a back-fill of contaminating particles from the throttle valve is prone to occur. Therefore, to ensure a constant and efficient exhaust is critical to processes involving a vacuum condition.
In view of the prior art described above, an apparatus and a method for securing a constant and efficient exhaust and reducing the activity frequency of throttle valve to improve the product reliability and promote the yield are highly desirable.
The present invention is directed toward a method and an apparatus for regulating exhaust pressure in an evacuation system of a semiconductor process chamber. The key aspect of the present invention is to maintain the equilibrium of the chamber pressure and the exhaust pressure by implementing an exhaust controller to control the gas flow rate introduced into the evacuation system. In other words, when the chamber pressure is increased, the extra gas is introduced into the evacuation system at an increased flow rate. On the other hand, when the chamber pressure is decreased, the extra gas is introduced into the evacuation system at a decreased flow rate. The dynamic control over the gas introduced into the evacuation system advantageously increases the speed of response during the changes of chamber pressure, as well as active control of the chamber pressure in place of moving the throttle valve. Thus, by minimizing the movement of throttle valve, the chances of particulate contamination of the process are greatly reduced.
It is another object of this invention that a method and an apparatus for reducing the activity frequency of the throttle valve are provided.
It is a further object of this invention that a method and an apparatus for optimizing the equilibrium of the chamber pressure and the exhaust pressure are provided.
It is another further object of this invention that a method and an apparatus for securing a constant and smooth exhaust that prevents the reflux of contaminants from inducing product defects are provided.
In accordance with the present invention, in one embodiment, an apparatus for regulating exhaust pressure in a semiconductor process chamber is provided. The apparatus comprises a vacuum pump, a first pressure sensor, a second pressure sensor, and a controller. The vacuum pump has an exhaust side and an intake side through a throttle valve coupled with the semiconductor process chamber for generating a first pressure in the process chamber and an exhaust pressure in-between the throttle valve and the intake side, wherein the first pressure is monitored by the first pressure sensor generating a first signal. The second pressure sensor is for monitoring the exhaust pressure in the intake side and the throttle valve to generate a second signal. The controller responsive to the first signal and the second signal regulates the exhaust pressure in the intake side, wherein the first pressure is higher than the exhaust pressure. The apparatus further comprises a gas port positioned upstream (or the intake side) of the vacuum pump. The controller regulates the exhaust pressure by controlling a gas flow rate introduced through the gas port. A method for regulating exhaust pressure in an evacuation system of a semiconductor process chamber is also provided. The method comprises steps of generating a first pressure in the semiconductor process chamber and an exhaust pressure in-between the process chamber and the evacuation system, monitoring the first pressure to generate a first signal, determining a set point for the exhaust pressure responsive to the first signal, and regulating the exhaust pressure by a controller till reaching the set point, wherein the first pressure is higher than the second pressure. The set point for the exhaust pressure can be pore-stored in the exhaust controller related to the chamber pressure. That is, every chamber pressure has a corresponding value for the exhaust pressure. The controller regulates the exhaust pressure by controlling a gas flow rate introduced through the gas port.